The present invention relates generally to methods and devices for cardiac surgery, and specifically to methods and apparatus for myocardial revascularization.
Myocardial revascularization is a technique, known in the art, for creating channels in ischemic heart tissue to improve the blood supply to ischemic myocardium. It may be performed by various techniques, the best-known of which is laser myocardial revascularization, which employs laser radiation for generating such channels.
In transmyocardial revascularization (TMR), as is known in the art, a computer-controlled laser is used to drill penetrating holes about 1 mm in diameter in the myocardium by delivering laser energy to the epicardium through an incision in the chest and the pericardium. Blood at the outer, epicardial openings of the channels typically clots after a few minutes, but the inner portions of the channels, communicating with the ventricle, remain patent. It is hypothesized that during systole, blood flows through these channels into naturally-existing myocardial sinusoids, supplementing the impaired arterial blood supply.
According to another hypothesis, the local injury caused to the myocardium by various forms of energy (e.g., laser radiation, as described above, or alternatively, RF radiation, or ultrasonic or mechanical energy) stimulates local angiogenesis, eventually supplementing the impaired arterial blood supply. Although there are no conclusive answers at present regarding the underlying mechanism, there is clinical evidence of the treatment""s therapeutic efficacy.
U.S. Pat. No. 5,389,096, to Aita, et al., which is incorporated herein by reference, describes methods and apparatus for percutaneous myocardial revascularization (PMR). A deflectable, elongated lasing apparatus is guided to an area within the patient""s heart, and the distal end of the apparatus is directed to an area of interest in the inner wall of the heart. The wall is irradiated with laser energy to form channels therein, preferably without perforating the epicardium. Alternatively, PMR may be carried out by applying other energy forms, as described above, from inside the art.
In TMR, as is known in the art, the channels are created through the myocardium from the outside in, and the transient blood stream ensuing upon channel completion constitutes an intrinsic indication of successful drilling. In PMR, however, the channel is generated from inside the heart chamber and, preferably, does not penetrate the myocardium. Consequently there is no direct indication of successful generation of the channel.
A PMR procedure, whether employing laser energy or any other suitable energy form, may fail due to a multiplicity of reasons. For example, referring specifically to laser PMR, the catheter inserted into the heart may be incorrectly oriented, so that the energy does not impact and penetrate the endocardium, or does not penetrate to a significant depth. Alternatively, the distal end of the catheter may be obstructed, for example, by a thrombus and/or ablated tissue residues. Because systems for PMR known in the art do not give any indication of whether the energy pulse has successfully generated a channel in the myocardium, it is difficult or impossible for an interventional cardiologist to detect and correct such a failure during the procedure.
It is an object of some aspects of the present invention to provide a reliable indication as to whether an energy pulse locally imparted to the heart has successfully produced a channel in the myocardium.
It is a further object of some aspects of the present invention to provide methods and apparatus for monitored PMR.
In the context of the present patent application and in the claims, the term xe2x80x9cPMRxe2x80x9d is taken to refer to any and all techniques of percutaneous myocardial revascularization treatment, including laser, RF, ultrasound and mechanical methods, but not limited thereto. Accordingly, while preferred embodiments of the present invention are described herein largely in terms of creating channels in the myocardium using laser irradiation, those skilled in the art will understand that the principles of the present invention are similarly applicable to other PMR techniques.
Some aspects of the present invention are based on the finding by the inventors that when an energy pulse is incident on the myocardium in such a manner as to create a channel therein, it causes detectable variations in the heart""s electrical activity, both local and global. In particular, the applicants have observed such variations when a laser beam creates a channel in the myocardium.
The local variation is expressed in the form of an elevated ST segment in the locally-measured electrogram. The elevated ST is characteristic of injuries to the heart, and is observed to last for at least several minutes after generating the channel. It is a distinctly local effect, and is not observed outside a diameter of several millimeters (typically 3 mm) from the point at which the channel is generated.
The global variation is observed in the form of disturbance of the heart""s sinus rhythm, typically in one or more ventricular premature beats (VPB""s) immediately following the laser pulse. The VPB""s are observed both in electrogram signals recorded within the heart chamber and in ECG signals recorded on the body surface.
It is still another object of some aspects of the present invention to provide indication that the channels have been generated in accordance with predetermined dimensions, location and orientation. These aspects of the invention are based primarily on the ability of ultrasonic waves to resolve zones of differing tissue characteristics, in particular density, thus imaging the channels"" dimensions and direction.
Other aspects of the present invention use real-time sensing technologies, particularly based on optical sensing, for detecting local changes in blood perfusion. By comparing pre- and post-PMR optical signals, enhanced blood perfusion of ischemic zones, due to successful channel generation, may be observed.
Some preferred embodiments of the present invention are based on a PMR catheter as described in PCT patent application no. PCT/IL97/00011, filed Jan. 14, 1997, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. The catheter comprises a waveguide, for conveying energy to the endocardium, preferably laser energy, and has at least one sensor at its distal tip. The sensor may comprise one or more electrophysiological sensing electrodes, position sensors, ultrasound transducers, or other sensors known in the art.
In some of these preferred embodiments, the sensor comprises an electrode, which receives electrical signals from the heart indicative of the efficacy of local PMR treatment, i.e., whether an energy pulse or series of pulses has actually succeeded in generating a channel of substantial depth in the myocardium. The catheter is coupled to signal processing circuitry, which processes the signals received by the electrode and provides an indication to a user of the catheter, typically an interventional cardiologist, as to whether the channel has been generated. The indication is typically based on elevation of the ST segment and/or VPB""s in the local electrogram during at least several minutes after the channel has been generated. Failure to sense such a change after one or several energy pulses is taken to be an indication of an error or malfunction, requiring the cardiologist""s intervention. Preferably, the catheter is held in place at a candidate site for a period both before and after channel generation, long enough to gather pre- and post-PMR electrograms, which are compared to ascertain the efficacy of the local treatment.
Preferably, the elevated ST effect, which is of a highly localized nature and significantly long duration, also provides an indication to the user during subsequent PRM channel generation as to whether a channel preexists in a new candidate area.
In some of these preferred embodiments, the electrode is used for gating the energy source, as described in PCT patent application no. PCT/IL97/00011, mentioned above, as well as sensing signals indicative of successful channel generation.
In some preferred embodiments of the present invention, ECG is measured during the PMR procedure by means of skin electrodes. Disturbances of the normal sinus rhythm, particularly ventricular premature beats (VPB""s), are sensed as an indication that an energy pulse has successfully generated a channel in the myocardium. Absence of such disturbance is, similarly, taken to indicate error or malfunction.
In other preferred embodiments of the present invention, the sensor at the distal end of the catheter comprises an ultrasonic transducer. The transducer generates signals responsive to the changes induced in the myocardial tissue by the channel generation operation. The signals are used to detect successful generation of the channel, alone or in conjunction with internal or external ECG readings.
Preferably, the ultrasonic signals are further used to monitor the depth and/or direction of the channel generated by the radiation.
In further preferred embodiments of the present invention, the sensor at the distal end of the catheter comprises a blood flow sensor, preferably an optical sensor or, alternatively, an ultrasonic sensor, which generates signals responsive to local microcirculation blood flow. The signals are used to detect successful reperfusion at the treated site.
In alternative preferred embodiments of the present invention, the sensor at the distal end of the catheter comprises an optical sensor, which receives light emitted by endocardial tissue. Light is transmitted from a radiation source, optionally via the waveguide in the catheter, as described above, to the myocardial tissue. The radiation is tuned to be absorbed by substances in the tissue related to local blood perfusion and stimulate them to fluoresce (i.e., autofluorescence). The emitted autofluorescent radiation is received by the optical imaging sensor and is measured to detect successful channel generation. For example, the sensor may be used to detect local NADH levels, which are correlated with ischemia, as described in a series of publications, including Kedem et al., Q. J. Exp. Physiol. 66:501-514, 1981; Furman et al., Cardiovasc. Res. 10:606-612, 1985; and Duboc et al., Lancet, Aug. 30 1986, p. 522, which are incorporated herein by reference.
Alternatively, fluorescing contrast agents, known in the art, such as fluorescein or indocyanine green (ICG), may be injected into the blood stream to facilitate photo-detection of local blood perfusion by angiography. Such methods are described, for example, in U.S. Pat. No. 5,566,673, to Shiono, and in an article by May in Biophotonics International, May/June 1995, pp. 44-50, which are incorporated herein by reference.
Although preferred embodiments are described herein with reference to certain types of PMR catheters, in particular those described in the above-mentioned PCT patent application no. PCT/IL/00011, it will be appreciated that the principles of the present invention may similarly be applied using other types of catheters and apparatus, as are known in the art. In particular, as noted above, the catheter may comprise a device for imparting to the heart energy forms other than laser radiation, for example, RF, ultrasonic or mechanical energy.
There is thus provided, in accordance with a preferred embodiment of the present invention, apparatus for PMR treatment, including:
an elongate probe having a distal end for engaging heart tissue of a subject, and including a revascularization device, which imparts energy to the heart tissue for generating perfusion-enhancing channels therein; and
a sensor, which provides an indication responsive to the treatment.
Preferably, the sensor receives signals generated by the body of the subject responsive to the treatment.
Further preferably, the sensor includes an electrode, which is positioned on the probe adjacent the distal end thereof.
Alternatively or additionally, the electrode is placed on the subject""s body independently of the probe.
In preferred embodiments, the sensor includes a transducer, preferably an ultrasonic transducer, which generates signals indicative of the treatment.
Alternatively or additionally, the sensor includes a blood flow sensor, which generates signals responsive to microcirculation.
Preferably, the transducer is positioned on the probe adjacent the distal end thereof.
In another preferred embodiment, the sensor includes an optical sensor, and the apparatus preferably includes a waveguide, which transmits fluorescence-stimulating radiation to the myocardial tissue, wherein the sensor receives fluorescence emitted from the tissue and generates signals indicative of the treatment.
Preferably the apparatus includes signal processing circuitry, which is coupled to the sensor and analyzes the signals to provide an indication of the efficacy of the treatment. Preferably, the circuitry detects an elevated ST segment or, alternatively or additionally, an arrhythmia. Preferably, the arrhythmia detected by the circuitry includes at least one VPB.
Alternatively or additionally, the circuitry detects a change in tissue characteristics adjacent to the distal end of the probe. Preferably, the change includes a change in tissue density, or, alternatively or additionally, an increase in blood perfusion adjacent to the distal end of the probe.
Preferably, the revascularization device applies laser radiation to the heart tissue.
Alternatively, the revascularization device applies RF energy, high-intensity ultrasonic radiation, and/or mechanical energy to the heart tissue.
There is also provided, in accordance with a preferred embodiment of the present invention, a method for monitored PMR treatment of the heart of a subject, including:
bringing a probe, including a revascularization device for imparting energy to the heart, into engagement with heart tissue of a subject;
imparting energy to the heart tissue using the device so as to generate perfusion-enhancing channels therein; and
receiving a signal from the body of the subject responsive to the treatment.
Preferably, receiving the signal includes receiving a signal generated by the body of the subject indicative of successful performance of the treatment.
Further preferably, sensing the signal includes sensing an electrical signal inside the heart of the subject, or,
alternatively or additionally, on a surface of the body of the subject.
In a preferred embodiment, receiving the signal includes receiving energy reflected from the heart tissue, preferably ultrasonic energy reflected from a designated channel location within the heart.
In another preferred embodiment, receiving energy includes receiving fluorescence radiation emitted from the heart tissue, preferably autofluorescent radiation or, alternatively, from an agent administered into the subject""s blood stream.
In still another preferred embodiment, receiving the signal includes receiving signals responsive to microcirculation blood flow rate adjacent a designated channel location within the heart.
Preferably, the above method includes processing the signals to provide an indication of the efficacy of the treatment, most preferably by detecting an elevated ST segment, or alternatively or additionally, by detecting an arrhythmia. Preferably, detecting the arrhythmia includes detecting a VPB.
In a preferred embodiment, processing the signals includes detecting changes in tissue characteristics in the channel area, preferably detecting changes in tissue density.
Alternatively, processing the signals includes detecting changes in blood perfusion in the tissue, preferably, detecting an enhancement of the perfusion.
Preferably, imparting energy to the heart includes imparting laser radiation.
Alternatively, imparting energy to the heart includes imparting RF radiation, high-intensity ultrasonic radiation, or mechanical energy.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: